This invention pertains to bottles for holding liquids, and in particular the invention concerns one piece, self-standing, plastic bottles suitable for containing carbonated beverages or other liquids under pressure.
Until more recent years liquids have been stored primarily in various containers made of metal, ceramics and glass. Many liquids sold to consumers have been contained in transparent bottles and this is particularly true with respect to liquid products that are destined for human consumption. Glass bottles have been used in great abundance for many years as containers for such liquids, but these vessels have a number of unattractive properties. For example, glass bottles are fragile which may lead to container breakage resulting in product and container loss, and even bodily injury. The bottles are heavy and cause substantial expenditures in energy during manufacture and transportation.
These and other considerations have caused many products to be stored in plastic containers which may be transparent, translucent or opaque. The type of plastic used in making these containers is chosen according to the properties needed to hold liquids of given types. For liquids under essentially atmospheric pressure, the shape of the container and its manufacturing procedure may vary considerably. Also, a number of plastics meet the physical and chemical requirements under these circumstances, and the use of the least expensive plastic becomes a primary consideration in selecting the type of plastic used. The shape of the bottle may be varied widely depending on factors such as liquid capacity, cross-sectional area of the container and attractiveness to the consumer. However, in the case of liquids held under elevated pressure, the choices in various respects can be materially lessened. Thus, the shape of the container or bottle is generally the strongest cylinder, i.e. an essentially circular cylinder, and the plastic bottle is formed by biaxial orientation which develops the strongest side walls which, due to economic considerations, are generally quite thin. In order that the bottle will retain its shape when stored with its liquid contents under pressure, the composition of the plastic is chosen to have sufficient creep resistance, and may be, e.g., polyethylene terephthalate (PET), styrene-acrylonitrile copolymers, polycarbonates, polysulfones, polyvinyl chloride and the like.
In order that the plastic bottle be the most convenient to manufacture and of lower cost, it is desired to obtain a one piece, self-standing bottle. The nature of the bottom of the bottle is very important, not only because it is most desirable that the bottle stand upright on a generally flat surface, but also because the bottom is subjected to bending moments which tend to distort the shape of the bottom and make the bottle unstable in standing upright. The bottom must, therefore, adequately resist the bending forces in order to remain standing. A cylindrical bottle having the greatest volume with the use of the least amount of plastic material would have a hemispherical bottom, but, of course, such a bottle will not free-stand in the upright position. Although the bottom of the bottle may have somewhat greater thickness than the sidewall of the body of the bottle and thereby have greater strength and resistance to gas permeation, the shape of the bottom may distort under the stress of the liquid and gas pressure in the bottle. If the bottle originally has a flat-bottom that becomes distorted when stored with its liquid contents under elevated pressure, the bottle, if it does not fracture, will become unsteady and may topple. Such bottles are commonly referred to as "rockers". Plastic bottle bottoms of other shapes may also distort and become rockers under various conditions of storage and use.
Although there have been quite a number of prior proposals regarding the configuration of the bottoms of one-piece, self-standing, plastic bottles for containing pressurized liquids, relatively few have appeared on the market. Some of these were not particularly stable and had liquid capacities of at least about one liter, say up to about 2 liters or so.
In the past the design of one-piece plastic bottles suitable for elevated pressure use has led to relatively high manufacturing costs due, for example, to the use of a relatively large amount of plastic for a given volume of bottle and, quite importantly, to slow manufacturing procedures. Major attention has been given to obtaining improvements in the stability, or non-everting, properties of the bottom of the single piece, free-standing bottles. Designs such as those described in U.S. Pat. Nos. 3,598,270; 3,727,783; 3,871,541; 3,935,955; 4,108,324; 3,718,229; 3,722,726; 3,881,621 and 4,134,510 are relatively complicated with, for example, reinforcing ribs and reverse directing arcs. In general, these designs require high forming pressures and longer equipment cycle times. Further, the more complicated designs inhibit uniform biaxial orientation during bottle forming and reduce the material efficiency usage, i.e. it requires more material to produce a bottle bottom that does not evert at the higher range of use temperatures and pressures.
Other simpler bottle designs such as those shown in U.S. Pat. Nos. 3,759,410; 3,511,401; 3,643,829; 3,811,588; 3,870,181 and 3,934,743 employ plastic materials, e.g. acrylonitriles, acrylates or polyvinylchlorides. Generally, these designs require heavier walls to retain their shape at the higher use stress and temperature levels. Further, the costs of the materials are relatively high.
In summary, the simpler, non-everting, carbonated beverage bottle designs of the prior art generally apply to more expensive plastics while more complicated, less material efficient and more difficult to form designs have been proposed for producing non-everting, free-standing carbonated beverage bottles from materials such as polyethylene terephthalate.
The one-piece bottles have been made by blow molding techniques employing a preformed parison, and the speed of this operation is controlled by heating and cooling rates and other factors such as the ease of forming the shape needed and the facility with which the bottle can be removed from the forming mold. In the case of relatively large bottles of say 2 liter-capacity, the overall cost of making one-piece bottles may be greater than for two-piece bottles, even though the latter require additional manufacturing steps and a greater number of bottle parts. Therefore, the challenge of economically making one-piece, plastic bottles has remained, and is particularly acute in the area of bottles of about one liter in capacity. In the latter case, the manufacturing cost is even more important since the volume of liquid contents sold per unit container is reduced while the amount of plastic material utilized per unit of liquid content is increased.
As bottle size decreases its surface to volume ratio increases. This relationship dictates heavier average walls for the bottle to retain a specified percentage of original gas content. In addition, as bottle size decreases, the degree of biorientation in the bottle wall becomes more difficult to achieve since there are shorter available distances for material stretching while forming the bottle from the parison, and since the heavier walls required to retain the gas content dictate less draw-down from the parison dimensions. Thus, in smaller bottles there tends to be less orientation and thus less resistance to creep than in larger bottles of similar wall thickness. The efficiency of material usage in smaller bottles is, thus, significantly less than in larger bottles.
These difficulties have led to greater use of the two-piece, larger plastic bottles for holding liquids under pressure, e.g. carbonated beverages, particularly soft drinks. The main portion of the upper piece of the bottle is a biaxially oriented, synthetic resin or plastic structure having an essentially circular cross-section and a spherical bottom, see U.S. Pat. Nos. 3,722,725 and 3,948,404. In order to make the bottle stand upright on its lower end opposite the cap, the spherical bottom of the bottle is held in a round cup having a generally flat bottom. Such cups involve additional expense and manufacturing procedures, and the cups are subject to breakage or loss from the bottle.
The present invention is directed to one-piece, self-standing, biaxially-oriented, plastic bottles suitable for holding liquids under pressure, for example, carbonated beverages, over a shelf-life satisfying commercial standards of performance and cost. The bottles have an integrally-formed bottom that is constructed in a manner maximizing the strength, toughness, uniformity of orientation, and standing stability of the bottle on its lower end. Any creep of the bottle during storage usually is insufficient to cause the bottle to evert or fall on its side or even to become a rocker. Moreover, the shape of the bottle minimizes the amount of plastic material that need be employed in forming a bottle of given capacity and strength, i.e. there is good material efficiency. In making the bottle the speed of manufacture is markedly improved, e.g. the molding cycle is shorter, compared with many prior one-piece plastic bottles destined for such use. In now appears quite feasible to manufacture the bottles of the invention economically, even bottles that do not exceed about 1 liter in liquid capacity.
The bottles of the present invention are characterized by several features including a bottom having surface portions that are approximately spherical. The bottom of the bottle is spherical and contains a plurality of lobes or feet extending downwardly on the outside surface and around the periphery of the bottom. The feet have a substantially spherical lower portion and the horizontal diameter of the feet has its outer end substantially in line with the vertical sidewall of the main body of the bottle, and as a result the bottle has good standing stability. Thus, the outer sidewall of the upper part of the feet above the lower, spherical portion of the feet is in essence a vertical extension of the sidewall of the body of the bottle.
The feet are formed from, and are therefore extensions of, the relatively thicker spherical bottom. The feet have relatively thin walls compared with those of many prior bottles, and the stretching of the plastic in forming the feet results in good biaxial orientation. The outer periphery of the spherical feet, or a vertical extention of the outer periphery, intersects the spherical surface of the bottom of the bottle. Thus the tops of the feet do not flare outwardly from the maximum diameter of their spherical bottom, except, if desired, in the vicinity of the intersection with the bottom of the bottle. As a result, the vertical extensions of the feet are narrower at their tops than along their sides when viewed from the outer sides and from this standpoint the feet may be considered to be generally similar in shape to a teardrop. An advantage in this structure is that the bottom of the bottle does not undergo the extent of stretching that would be required if the tops of the feet flared outwardly, and, as a result, for a given bottom thickness the feet formed from the bottom are stronger and more uniform in thickness and orientation. The feet are, thus, formed with good material efficiency and exhibit high impact strength. The number of such feet on the bottom of the bottle is at least 3 or 4, preferably at least 5, say up to about 9, especially 5 to 7. A greater number of such feet does not seem particularly advantageous, and the expense of a more complicated mold needed to form the bottle has not been found to be justified.
The dimensional and structural relationships stated herein can be taken as referring to the mold in which the bottle is shaped as well as the actual bottle. The shape of the bottle may vary somewhat due, for example, to minor inconsistencies or variations in the molding process and to shrinkage of the bottle during cooling. The mold may be shaped to allow for such shrinkage.
The simplicity of the design of the bottle of the invention employing a spherically-shaped bottom with spherical extensions to provide standing stability permits the fullest application of the surface-to-volume ratio efficiency of spheres. This configuration provides maximum toughness, minimum permeability and minimum creep to be achieved with the least amount of plastic utilization. In addition, the shape of the bottom facilitates uniform biorientation and formability, since material movement in the bottom emanates essentially unobstructedly from a single center, i.e., that of the principal base sphere.
The feet of the bottle of the invention are of substantially circular cross-section and are spaced-apart from one another around the periphery of the bottom of the bottle in a manner that provides a surface between adjacent feet having a shape approximating the principal spherical surface of the bottom. The feet thus have relatively small diameters. It is preferred that the upper sidewall of the feet merge as a radius into the principal surface of the spherical bottom, except for the outermost portion of the upper sidewall of the feet which is more or less directly below the wall of the body of the bottle. Thus, the outermost wall portion of the feet is in essence a vertical, extension of the sidewall of the body of the bottle as noted above. A portion of the principal spherical surface of the bottom of the bottle is positioned interiorly of the feet.
Although the principal spherical surface of the bottom of the bottle of the invention may extend more or less throughout the central area interiorally of the feet, from the aesthetic and standing-stability standpoints this may be unattractive. Accordingly, the center portion of the bottom of the bottle may be depressed inwardly relative to the principal spherical surface of the bottom and this will provide greater clearance from a surface on which the bottle stands to insure that some growth or creep of the bottle will not extend the center portion of the bottom to below the lowermost portions of the feet to upset the bottle or produce a rocker upon storage with pressurized liquid therein.
The configuration of the one-piece bottle of the invention provides a bottom with satisfactory strength and the bottle is resistent to undue deformation that could otherwise cause the bottle to become a rocker and even topple when standing on the feet. The portions of the feet in contact with a generally flat or somewhat inclined surface on which the bottle stands are positioned relatively close to the outer periphery of the bottle due to the relatively small diameter of the feet. This configuration increases the standing stability of the bottle. Yet the bottle can be made by blow molding at relatively fast rates using a mold of simple configuration compared to some structures that have theretofore been proposed. The shape of the bottom of the bottle permits the use of a minimum amount of plastic in forming the bottle. These and other advantages of the bottle of the invention as stated above become apparent from the following detailed description of the bottle and the drawings.